revent: Handlers default to priority 0 (not None)

Previously, handlers defaulted to priority None, which is less than any
integer, so they'd always be called last.  This meant that it wasn't
possible to set another handler to be called *after* a default one (not
reliably, anyway).  Now, handlers default to priority 0, so it's totally
possible -- just add handler with priority -1.

The cost here is mostly an extra hash lookup at handler-add time.  This
could be swapped for an extra list lookup at add and event-raise time...

Author: MurphyMc

pox/lib/revent/revent.py

@@ -100,6 +100,8 @@ def foo (self):
 # handler set will not keep the source (publisher) alive.
 import weakref
 
+DEFAULT_PRIORITY = 0
+
 
 class ReventError (RuntimeError):
   """
@@ -228,6 +230,10 @@ def _eventMixin_init (self):
       setattr(self, "_eventMixin_events", True)
     if not hasattr(self, "_eventMixin_handlers"):
       setattr(self, "_eventMixin_handlers", {})
+    if not hasattr(self, "_eventMixin_prioritized"):
+      setattr(self, "_eventMixin_prioritized", set())
+    #TODO: Avoid extra hash lookup by putting priority info on
+    #      the list of handlers instead of separate attribute.
 
   def raiseEventNoErrors (self, event, *args, **kw):
     """
@@ -388,7 +394,7 @@ def addListenerByName (self, *args, **kw):
     return self.addListener(*args,**kw)
 
   def add_listener (self, handler, event_type=None, event_name=None,
-                    once=False, weak=False, priority=None):
+                    once=False, weak=False, priority=DEFAULT_PRIORITY):
     """
     Add an event handler for an event triggered by this object (subscribe).
 
@@ -407,7 +413,7 @@ def add_listener (self, handler, event_type=None, event_name=None,
                             priority=priority)
 
   def addListener (self, eventType, handler, once=False, weak=False,
-                   priority=None, byName=False):
+                   priority=DEFAULT_PRIORITY, byName=False):
     """
     Add an event handler for an event triggered by this object (subscribe).
 
@@ -464,8 +470,10 @@ def addListener (self, eventType, handler, once=False, weak=False,
     entry = (priority, handler, once, eid)
 
     handlers.append(entry)
-    if priority is not None:
+    if ( (priority != DEFAULT_PRIORITY) or
+        (eventType in self._eventMixin_prioritized) ):
       # If priority is specified, sort the event handlers
+      self._eventMixin_prioritized.add(eventType)
       handlers.sort(reverse = True, key = operator.itemgetter(0))
 
     return (eventType,eid)
@@ -481,7 +489,8 @@ def listenTo (self, source, *args, **kv):
     """
     return autoBindEvents(self, source, *args, **kv)
 
-  def addListeners (self, sink, prefix='', weak=False, priority=None):
+  def addListeners (self, sink, prefix='', weak=False,
+                    priority=DEFAULT_PRIORITY):
     """
     Automatically subscribe sink to our events.
 
@@ -499,7 +508,8 @@ def clearHandlers(self):
     self._eventMixin_handlers = {}
 
 
-def autoBindEvents (sink, source, prefix='', weak=False, priority=None):
+def autoBindEvents (sink, source, prefix='', weak=False,
+                    priority=DEFAULT_PRIORITY):
   """
   Automatically set up listeners on sink for events raised by source.